There are no clear methodologies regarding the flow rate and route of administration of drugs into a hard-shell venous reservoir during extracorporeal circulation, making it important to understand the characteristics of drug diffusion in the hard-shell venous reservoir that is used. An assessment of drug diffusion is difficult because there is no established method for evaluating these characteristics and evaluations can only be performed based on the operator's existing knowledge, experience, expertise, or familiarity with injecting drugs into the hard-shell venous reservoir being used. Therefore, in this experiment, we developed an analytical model to assess changes in the concentration of drug solution flowing out of four types of hard-shell venous reservoirs, conducted basic experiments by changing the liquid levels, and investigated a method for evaluating the performance of hard-shell venous reservoirs in terms of diffusion of the drug solution. The results of the basic experiments showed that there was little difference in drug diffusion performance between the four types of hard-shell venous reservoirs used in the experiments. In addition, when the fluid level was 500 mL or less, evaluation of the performance of drug diffusion could be conducted using the time constant based on the analytical model, but when the fluid level was 1000 mL or more, the rise-time was better than the time constant. In future research, based on this experimental method, we would like to evaluate the drug diffusion performance of hard-shell venous reservoirs by changing the following: (1) flow rate in the circuit, (2) the location of drug administration, and (3) the flow rate of injected drugs. Key words: hard-shell venous reservoir,drug diffusion,venous reservoir level,time constant,rise time [原稿受領日:2021 年 11 月 29 日 採択日:2022 年 4 月 9 日] 1)藍野大学 医療保健学部 臨床工学科 畑中由佳(Yuka Hatanaka) 〒 567-0012 大阪府茨木市東太田 4-5-4